Some high performance engines that are used in race cars have so much power that there is a likelihood of the wheels of the car spinning against the pavement during acceleration. When the wheels of a vehicle spin, the lost traction between the wheels and the road results in lost acceleration performance of the vehicle.
In order to avoid the spinning of the wheels during acceleration of a racing vehicle the manufacturers of carburetors have developed progressive butterfly valve linkages that begin opening the primary butterfly valves before the secondary butterfly valves are opened. When the primary butterflies have been opened to a predetermined degree, more movement of the linkage continues the opening of the primary butterflies and begins to open of the secondary butterfly valves. With this progressive linkage arrangement, the application of too much power immediately upon the start of throttle treadle travel can be avoided, and the driver can continue to depress the accelerator to progressively open the secondary butterflies.
It is desirable to be able to change the performance of the progressive linkage of the carburetor so as to enable the driver to have longer performance of the engine with only the primary butterflies open, and then later open the secondaries. For example, on a slicker track, the driver is likely to want to continue with the progressive opening of only the primary butterflies to allow the vehicle to accelerate more slowly without loss of traction, and then open the secondary butterflies after a desirable speed has been reached. Conversely, if the race track conditions are such that the driver is not concerned with loss of traction during the early performance of the engine, it would be desirable to modify the progressive linkage so that the secondary butterflies of the carburetor would open earlier during the progressive opening of the primary butterflies.
In the past, there have been two primary methods that allowed for the modification of the timing between the primary butterfly valves and the activation of the secondary butterfly valves of a carburetor. One method required the mechanic to loosen the screws that connect the parts of the linkage together, remove the part and then substitute a new part of a different shape in the linkage. This is somewhat cumbersome and tedious for the mechanic, and there is a hazard that the screws that connect the parts together may be dropped and lost in the engine of the vehicle, and replacement screws must be used.
The second method consisted of a link and pin system. To change the secondary timing, a cotter pine (or like retention device) needed to be removed and the link changed and installed in a different location, and the cotter pine re-installed. Again, this is somewhat cumbersome and tedious to the mechanic, and there is the hazard that the link or pin can be dropped or lost.
Accordingly, it would be desirable to provide a carburetor with a progressive linkage that can be quickly changed so as to modify the degree of opening of the primary butterfly valves prior to the initiation of the opening of the secondary butterfly valves in order to enhance the performance of the vehicle on various track surfaces.